1. Field of the Invention
The present invention relates generally to electrical machine drive systems, and specifically, to a method and apparatus simulating fault modes and operational techniques for electrical machine drives for hybrid electric vehicles, electric vehicles and other systems.
2. Discussion of the Prior Art
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Also, hybrid electric vehicles (HEV), which combine a smaller ICE with electric motors into one vehicle, attempt to address these needs.
Understanding electrical drive fault affects is critical in the design of electric vehicles and hybrid electric vehicles. In particular, where permanent magnet electric motors are employed, diagnosis and mitigation of fault modes are critical. This is due in part to the continuous existence of permanent magnet flux, which may produce pulsation torque, over voltage or over current conditions during certain fault modes.
Known methods for evaluating fault modes and operational techniques include modeling electrical drive system fault modes with a set of complex differential equations; simulating the system to determine the effects of the fault; selecting a post fault control strategy; modeling the post fault control strategy with a different set of complex differential equations; and simulating the system to determine the effects of the post fault control strategy. Welchko, Brian A. et al., xe2x80x9cIPM Synchronous Machine Drive Response to a Single-Phase Open Circuit Fault,xe2x80x9dIEEE Applied Power Electronics Conference (APEC), Mar 4-8, 2001, Paper Number 13A. 1, pp. 1-7, and Welchko, Brian A. et al., xe2x80x9cIPM Synchronous Machine Drive Response to Symmetric and Asymmetric Short Circuit Faults,xe2x80x9dEPE 2001xe2x80x94Graz, pp. 1-10, are exemplary of the conventional modeling and simulation techniques. Unfortunately, these known methods require complex differential equations, which must be revised for each model and post fault control strategy. In many fault modes the differential equations cannot even be derived. In addition, these methods require long simulation time.
Therefore, a need exists for a simple method and apparatus for simulating fault modes in electrical machine drive systems.
Accordingly, an object of the present invention is to provide an apparatus and method that reduces the complexity of modeling operational modes for electrical machine drive systems in electric or hybrid electric vehicles.
Another object of the present invention is to reduce the simulation time required to model electrical machine drive operation.
Yet another object of the present invention is to provide a method and apparatus to readily improve electric and hybrid electric vehicle design through simulation of electrical machine drive operation.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.
In accordance with one aspect of the invention, an electrical machine drive system is provided. The system includes a DC power source, an inverter model, and an electrical machine model. The DC power source is coupled to and drives the inverter model. The electrical machine model is coupled to the inverter to be driven by the inverter. The electrical machine model includes a first winding, a second winding, a third winding, a first mutual inductor, a second mutual inductor, and a third mutual inductor. The first, second and third winding are coupled together at a node. The first mutual inductor reflects a mutual coupling between the first winding and the second winding; the second mutual inductor reflects a mutual coupling between the second winding and the third winding; and the third mutual inductor reflects a mutual coupling between the third winding and first winding. Each of the first, second and third windings includes: (1) a voltage source coupled to the node intermediate the first, second and third windings; (2) a phase inductor coupled to the voltage source; and (3) a phase resistor coupled to the phase inductor. Preferably, the phase inductance of the phase inductor and the mutual inductance of the mutual inductor vary as a function of rotor position. Also, the voltage source preferably varies as a function of speed and electromagnetic field density.
In accordance with another aspect of the invention, a method is provided for simulating an electrical machine drive system simulation model. The method includes the step of simulating a response of the electrical machine drive simulation model. Preferably, the method further includes the step of selectively inserting faults in the electrical machine drive system simulation model. Faults are alternatively inserted by opening a connection in the simulation model or shorting a connection in the simulation model. The fault insertion may include adding or deleting components.
A further aspect of the present invention includes an alternative method for simulating an electrical machine drive system. In this method, the electrical machine drive system simulation model is stimulated with a plurality of ideal sinusoidal voltage sources. This simulates a steady state of the model in a relatively short simulation time. Then, if needed, the ideal sinusoidal voltage sources are disconnected from the model and further simulation continues with the electrical machine drive system simulation model being driven by the battery and/or inverter. And, the inverter is in turn controlled by a variety of pulse-width modulation signal generators. This simulates a transient behavior of the model and requires relatively longer simulation time due to the high frequency response of the inverter switches.